It is well known that cardiac arrhythmias may be controlled with devices such as implantable defibrillators. Past approaches to electrodes used with such devices have employed endocardial electrodes as disclosed in Mirowski et al. U.S. Pat. No. 3,942,536 and Kinney et al. U.S. Pat. No. 4,161,952 or epicardial electrodes as disclosed in Heilman et al. U.S. Pat. No. 4,030,509 and Heilman et al. U.S. Pat. No. 4,291,707.
For systems using epicardial electrodes several functional requirements must be met. The electrodes must be able to deliver large amounts of electrical energy. Electrodes that have large surface areas are desirable since energy can be delivered over a larger area of the heart and current is distributed through greater electrode surface area. Thus current densities and the chance of damaging heart tissue is lessened. Past epicardial patch electrodes have used screens or mesh as disclosed in Heilman et al. U.S. Pat. No. 4,030,509, to accomplish this function.
The electrodes must be flexible enough to conform to the heart. Electrodes which are flexible are not only easier to manipulate and surgically implant, they are also more likely to conform to the heart thus ensuring reliable electrical contact with heart tissue.
The electrodes must be fatigue resistant. The environment that the electrode is in must endure constant motion and millions of flex cycles. Prior art patch electrodes have used space wound coils for flexibility and enhanced fatigue life as disclosed in Holleman et al. U.S. Pat. No. 4,971,070.
Other objects and advantages of the present invention will become apparent as the description proceeds.